When emulsion polyvinyl chloride and plasticiser are mixed a paste is typically formed which dries upon heating at temperatures above 160° C. to form a film. As the temperature is increased the polyvinyl chloride grains in the PVC composition begin to swell eventually forming a solid composition (dry film). This is known as the gelation temperature of the polyvinyl chloride composition and is typically in the range of 70° to 110° C. Fusion is the term that is used to describe the moment when the dry layer has developed its full mechanical or physical strength to form an integral article. The fusion temperature is typically in the range of 160° to 190° C.
The compositions are said to be useful in the manufacture of articles produced from conventional plastisol compositions including the manufacture of floor and wall coverings.
Polyvinyl chloride is available in two general forms known as suspension polyvinyl chloride and emulsion polyvinyl chloride according to their method of manufacture. Polyvinyl chloride that is used in plastisols, which are required to flow, is generally an emulsion polyvinyl chloride and this is typically used in the production of flooring and wall covering materials. Polyvinyl chlorides are classified as having a certain K value which is an indication of the mean molecular weight of the polymer. The higher the K value the better the mechanical properties like abrasion resistance of the polyvinyl chloride and the more useful the polyvinyl chloride in applications which are subject to abrasion such as in the top layer of flooring materials. However, the higher the K value of the polyvinyl chloride the slower the gelation rate, the higher the fusion temperature and the lower the flowability of the resin, which is undesirable for plastisol processing. Accordingly there is a need for fast gelling and fast fusing polyvinyl chloride compositions.
The properties required of a plasticiser vary according to the application in which the plasticised polyvinyl chloride composition is to be used. Typically this may be exemplified by the requirements of different layers in cushioned vinyl floor covering materials. The plastisol is spread on a surface moving at 15 to 25 meters per minute in several layers so that the floor covering is literally built up. Typically these layers include a glass matt impregnation layer, a foam core, a decorative layer and a clear protective surface wear layer. The multilayer products are first gelled by contact with a heated roll and then passed into an oven where they are fused at a temperature from 180° C. to 200° C. Often the gelling is performed after the spreading of each individual layer, starting with the base or encapsulation layer. The next layer cannot be applied until the previous layer has gelled. When all layers have been spread, the product is then passed into and through an oven to obtain full fusion of all layers and adequate expansion of the foamed layers.
To fulfil the plastisol spread coating requirements in terms of production speed, the PVC composition is required to be of low viscosity, exhibit a low gel temperature and a fast fusing rate.
In other applications such as the production of wall coverings, which typically consist of a compact foam layer on a paper backing, the machine speeds can be as high as 100 meters per minute and here the coating viscosity is important.
The presence of plasticisers tends to increase the susceptibility of the material to staining and hence it is desirable to minimise the amount of plasticisers present in the top coating to improve stain resistance and also to improve wearing properties.
However, as the plasticiser concentrations decrease, the viscosity of the paste PVC composition increases and it then becomes necessary to use increasing levels of viscosity depressants in the formulations in order to have the low viscosity required for the speed of the application. Stain resistance can also be improved by using faster-fusing plasticisers, which lead to a hardening effect on the surface of the finished product.
Despite the suggestion in WO 97/39060 that C13 alkyl benzoates may be used as viscosity depressants, hydrocarbons have continued to be used as viscosity depressants, as have certain low molecular weight esters such as texanol isobutyrate (known as TXIB available from Eastman Chemical Co). The use of these materials suffers from the disadvantage that they are volatile and can release volatile organic compounds (VOC), which can impair the ambient air quality in terms of odours and pollutants both during processing and in finished product use. Increased awareness of the indoor environment has created a demand for low-emitting building materials as evidenced by the European Building and Construction Directive and in particular the European ENV 13419.
A further disadvantage of the use of viscosity depressants such as TXIB and hydrocarbon fluids is that they have little if any plasticising effect in polyvinyl chloride formulations and have the tendency to increase the gelation temperature. Viscosity depressants with little plasticising effect such as TXIB are too volatile to have much of a plasticising effect.
A further factor is the nature of the primary plasticisers that can be used in the top layer of flooring. For faster processing of the flooring top layer, it is desired to obtain plastisol compositions with low gelation temperature and fast gelation rate. It is the reason why speciality plasticisers such as diisoheptyl phthalate and butyl benzyl phthalate have been used in combination with general purpose plasticisers like di-2-ethyl hexyl phthalate or diisononyl phthalate. These special plasticisers are, however, expensive and it has recently been suggested that di-2-ethyl hexyl phthalate and butyl benzyl phthalate should be labelled Cat. 2 for their potential hazards as reproductive toxicants. It would therefore be highly desirable if conventional plasticisers such as di-2-propyl heptyl phthalate, diisononyl phthalate or diisodecyl phthalate could be used in the top layer of floor covering materials.
EP-A-1415978 suggests that benzoates produced from decanol mixtures derived from C4 olefins can be used as viscosity-reducing and gel-accelerating softening agents to modify plastics such as polyvinyl chloride. The preferred benzoates consist of 50-99% 2-propyl heptyl benzoate and are said to have low volatility, good gelling capacity, good cold flexibilisation and low viscosity when used in plastics.
According to EP-A-1415978 the benzoates may be used with conventional plasticisers and Examples 1 to 6 of EP-A-1415978 show that the benzoates when mixed with Vestolit B 701 Polyvinyl Chloride emulsion and Vestinol 9 (diisononyl phthalate from Oxeno) produce plastisols that have comparable viscosity to those in which the benzoate is produced from the Exxal 10 alcohol available from ExxonMobil Chemical Company.
Example 7 of EP-A-1415978 compares the Tg of these two benzoates and suggests that the product based on 2-propyl heptanol may have improved low temperature performance. EP-A-1415978 therefore suggests to the person skilled in the art that Exxal 10 based benzoate is not suitable for the end-uses mentioned.
It has been the practice to use blends of different plasticisers and/or blends of plasticisers and viscosity depressants in order to obtain polyvinyl chloride plastisols with optimum properties. The formulator has sought to provide a plastisol which is fast-fusing and has a low viscosity combined with good staining performance whilst using as little plasticiser as possible to retain product stiffness (which is another important consideration in the production of vinyl floor covering). Consumers prefer stiffer products because this is often associated with higher quality.
In a layered composite material stiffness comes from the outside layer and total thickness. Furthermore, the formulator has sought to provide formulations that will yield products having improved flexibility. More recently, it has become important that the plastisols employed in such composites have a low volatility.
Traditionally, fast-fusing plasticisers have been used as plastisol components to increase the speed of fusing. Although these products have acceptable staining performance they are too volatile. If, however, they are used in combination with the less volatile bulk plasticisers such as diisononyl phthalate, the staining performance decreases (i.e. the staining is worse).
There therefore remains a need for plastisol compositions which are of low viscosity, have low volatility, have good staining performance, provide products with good low temperature flexibility and contain as little plasticiser as possible. In addition there is a requirement for a plastisol component for use with bulk plasticisers such as diisononyl phthalate to enable the bulk plasticiser to be used in applications where their reduced volatility would be of benefit providing they also have acceptable staining performance.
In addition there is a need for a plastisol component which not only functions to reduce the viscosity of the plastisol but also has a plasticising effect and furthermore does not increase the level of VOC's generated from articles produced from the plastisol.
There therefore remains the following needs for plasticised polyvinyl chloride compositions    i) a low viscosity plasticiser which can function as a viscosity depressant for plasticised PVC formulations, which also has a plasticising effect and which offers good compatibility with PVC;    ii) a viscosity depressant whose volatility is acceptable while having little to no VOC contribution in emissions as measured by the Flec test;    iii) a viscosity depressant which is not detrimental to the susceptibility of articles made from the polyvinyl chloride composition to staining;    iv) a viscosity depressant which, when used results in a lower gelling temperature and faster fusing of the polyvinyl chloride composition;    v) a viscosity depressant which enhances the foaming rate of foamable polyvinyl chloride compositions;    vi) a viscosity depressant which will enable the use of C9+ phthalates in applications where hitherto they have been less favoured or unacceptable because of their higher viscosity, poor gelation, and poor staining characteristics.
It is also important that any such material should not adversely impact other properties such as low temperature flexibility as measured by the Clash and Berg test.